The present invention relates to the field of pylons for attaching aircraft engines and more precisely relates to the improvement in the thermal resistance of an aft aerodynamic fairing of such an attaching pylon.
This kind of attaching pylon, also called engine mounting structure (EMS) enables an engine to be suspended below the aircraft aerofoil, this engine to be mounted above the same aerofoil, or even this engine to be assembled at the rear part of the aircraft fuselage.
The invention can be used on any kind of aircraft equipped with turbojet engines or turbo-propellers, or even any other kind of turbine engine.
An attaching pylon is generally provided to be the linking interface between a turbine engine and an aircraft aerofoil. It allows to transmit to the structure of the aircraft strains generated by the associated engine thereof, and also allows conveyance of fuel, electrical, hydraulic and air systems between the engine and the aircraft.
In order to ensure the transmission of strains, the attaching pylon includes a rigid structure also called primary structure, usually of the “caisson” type, that is formed by assembling upper and lower spares and side panels connected to each other through transverse stiffening ribs.
Furthermore, the device is provided with attaching means interposed between the engine and the rigid structure, these means usually including two fasteners, commonly called engine fasteners, as well as a device for recovering thrust strains generated by the engine.
Analogously, the attaching pylon generally includes another series of fasteners making up a mounting system interposed between the rigid structure and the aircraft aerofoil, this system usually consisting of two or three fasteners.
Besides, such a pylon is provided with a plurality of secondary structures ensuring segregation and maintenance of systems while supporting aerodynamic fairing elements, the latter generally taking the form of assemblies of panels mounted onto these structures. In a manner known to those skilled in the art, the secondary structures are different from the rigid structure in that they are not intended to ensure transfer of strains from the engine to the aircraft aerofoil.
Among the secondary structures, there is the aft aerodynamic fairing, also called “Aft Pylon Fairing” (“APF”), which ensures a plurality of functions among which it is to be noted the formation of a heat or fireproof barrier, and the formation of an aerodynamic continuity between the engine outlet and the attaching pylon. This fairing assumes a lower position when the engine is intended to be placed under the wing, and assumes an upper position when the engine is intended to be placed above the wing. An exemplary fairing known in the art is disclosed in document EP 2 190 739, the contents of which are incorporated herein by reference.
This aft aerodynamic fairing generally takes the form of a caisson structure comprising two side panels assembled together by inner transverse stiffening ribs spaced from each other in a longitudinal direction of the fairing, as well as a heat-shield floor which is generally fastened to the caisson structure by splicing. It is set out that the caisson structure is usually not closed opposite to the heat-shield floor, that is at the upper part when the engine is intended to be suspended below the aircraft aerofoil, since it is at this place that this structure comes to be connected onto the other pylon structures, in particular on the so-called rear secondary structure (RSS). Nevertheless, a spar for closing the caisson structure can however be provided opposite the heat-shield floor.
The side panels of the aft aerodynamic structure and the aft aerodynamic fairing, which are lying in the continuity of each other, are provided such that a cold air flow, such as the secondary flow of the engine when the same is a turbofan engine, externally conforms to the shape thereof because of the implantation of these side panels in the secondary flow annular channel of the engine and/or at the outlet of this channel.
The heat-shield floor in turn has an outer face provided such that a hot flow of engine combustion gases, also called exhaust gases, that can reach temperatures in the order of 540° C., conforms to the shape thereof these temperatures tending to increase with recent trends in developing techniques implemented in turbojet engines. Temperatures reaching about 750° C. are indeed contemplated in some aircraft turbine engines under development.
This increase in combustion gas temperature raises numerous problems in particular with respect to heat resistance of materials forming the heat-shield floor and differential heat expansion of these materials with respect to materials making up the fairing caisson structure.
The increase in the differential heat expansion of these materials leads in particular to an increase in mechanical stresses undergone by the devices for splicing this floor to the abovementioned caisson structure.